1. Field of the Invention
The present invention relates to a magnetic head and a magnetic read/write apparatus with the magnetic head mounted thereon and, more particularly, to a technique for reducing projection of a magnetic pole against the magnetic head toward a floating surface.
2. Description of Related Art
A semiconductor memory and a magnetic memory have been principally used as a storage apparatus. From the viewpoint of an access time, the semiconductor memory has been used as an internal storage apparatus; in contrast, from the viewpoint of a large capacity and non-volatility, the magnetic memory has been used as an external storage apparatus. In a recording medium for a magnetic disk drive, a magnetic thin film is formed on a glass or Al substrate. A unit having a function of electromagnetic conversion (i.e., a writing unit) has been used to write magnetic information in the recording medium, and further, another unit (i.e., a retrieving unit) utilizing a magnetoresistive phenomenon, a giant magnetoresistive phenomenon or an inductive phenomenon has been used to retrieve the magnetic information. The above-described writing unit and retrieving unit are essential constituent elements of a magnetic head.
FIG. 5 shows the general configuration of a magnetic disk drive. FIG. 5(1) is a plane view of the magnetic disk drive; and FIG. 5(2) is a cross-sectional view of the magnetic disk drive. A recording medium 2 (actually, a plurality of media 2-1 through 2-4 exist) is connected directly to a motor 3, and it has a function to rotate when information is input or output. A magnetic head 1 is supported by a rotary actuator 4 via an arm 7. A suspension 8 has the function of pressing the magnetic head 1 against the recording medium 2 at a predetermined load. The magnetic head 1 moves on the recording medium 2 according to the rotation of the rotary actuator 4, to be positioned at an arbitrary position, and thereafter, it fulfills each of the functions of writing and retrieving the magnetic information. Moreover, in order to process a signal to a VCM for actuating the rotary actuator or a drive signal to the motor or process a recording or retrieving signal, it is necessary to provide a signal processing circuit 5 and a recording/retrieving circuit 6, which are attached to the main body of the magnetic disk drive.
FIG. 6 shows the basic structure of the information recording unit and the information retrieving unit, which are mounted on the magnetic head 1. A writing unit 10 comprises a spiral coil 12, a pair of magnetic poles 14 and 15 which hold the spiral coil 12 therebetween and are magnetically coupled to each other, and a further magnetic pole 16 for determining the width of a track.
A retrieving unit 11 comprises a magnetoresistive effect element 19 and an electrode 20 for supplying a constant current to the element and detecting a change in resistance. Another pair of magnetic poles 17 and 18 hold the magnetoresistive effect element 19 and the electrode 20 therebetween, and function as upper and lower shields for shielding an unnecessary magnetic field at the time of a retrieving operation. The above-described writing unit and retrieving unit are formed on a magnetic head body 25 (i.e., a slider) via an underlayer 24.
Furthermore, a protective film 30 is formed on the retrieving unit and the writing unit for the purpose of secureness of the reliability of the above-described constituent elements. The objects of the function of the protective film 30 include maintenance of mechanical strength when the head floats over the medium and prevention of degradation of the constituent elements caused by corrosive atmosphere of outside air. In order to achieve the above-described objects, an alumina film has been generally used as the protective film. A thickness of the film is set to 5 μm or more for the purpose of the maintenance of mechanical strength. A thin metallic film is sometimes formed between the alumina film and the constituent elements in order to improve the adhesiveness of the alumina film. Alternatively, a resin film such as a resist is sometimes be formed, before the alumina film is formed, in order to flatten asperity caused by the structure of the constituent elements. Such a thin metallic film or a resin film has the function as an intermediate layer in forming the protective film.
Since the magnetic disk drive has the features of high reliability and a large capacity, it has been widely adopted in the storage devices that supports a current information technology society. An increase in information quantity in the information society has been astonishing. Naturally, improvement in performance as to speed-up has been required for the magnetic disk drive so as to process a large quantity of information in a short time.
Such speed-up of the magnetic disk drive can be achieved by increasing a recording frequency and the rotation speed of the medium (i.e., a relative speed between the head and the medium). At the present time, an apparatus in which a recording frequency in excess of 400 MHz and the rotation of the medium in excess of 15,000 rpm are achieved has been manufactured among machines called a high-speed magnetic disk drive. Moreover, the technique of high frequency recording has been greatly improved by introducing the techniques of the field of communications. In view of the high-speed rotation of the medium, a heat releasing design has been positively adopted to suppress heat generation caused by friction between air and the surface of the medium which becomes conspicuous at a high-speed rotation in excess of 10,000 rpm.
Under the above-described situation, if the recording frequency is increased up to 500 MHz or higher, the magnetic head and the recording medium come into contact with each other during a recording operation, thereby inducing a trouble of a crash of the magnetic head on the recording medium in an extreme case. The causality of such crash was the deformation of an element, which consists of magnetic poles disposed opposite to the surface of the recording medium (specifically, the magnetic poles 14, 15, 16, 17 and 18 shown in FIG. 6). Such deformation is a result of a thermal expansion by heat generated due to high frequency loss (i.e., the so-called iron loss and the so-called copper loss of the coil). As a result, the element projects from a magnetic head floating surface and the magnetic head comes into contact with the recording medium.
It has been found that such trouble occurs also in a small-sized magnetic disk drive (e.g., 2.5 type or 1.8 type), which does not basically require high-speed performance, in particular. This case is characterized in that the trouble has been caused by not the heat generated during the recording operation since the frequency is low but the temperature of environment in which the magnetic disk drive is used. That is to say, the small-sized magnetic disk drive is excellent in portability, so that it is sometimes used under the environment of high temperature. In this case, there has arisen a problem that a contact or a crash occurs between the magnetic head and the recording medium. This trouble caused by an increase in environmental temperature induces a trouble with the recording medium since the writing unit and the retrieving unit in the magnetic head are thermally expanded by the heat, and therefore, the magnetic poles 15, 16, 17 and 18 shown in FIG. 6 project from the floating surface of the magnetic head. The trouble caused by the environmental temperature in the small-sized magnetic disk drive is attributable also to a shorter distance (i.e., a floating quantity) between the recording medium and the magnetic head than that in a large-sized magnetic disk drive.
As described above, deformation with respect to the floating surface of the magnetic head in the writing unit and the retrieving unit or a phenomenon of the projection from the floating surface of the magnetic head by the heat (that is, the heat generated in the magnetic head per se and the heat of the environmental temperature) has made it difficult to satisfy the demand for a small floating quantity, which is required for achieving, in particular, high density recording. Specifically, it has been difficult to reduce a floating quantity down to so remarkably small a value as about 10 nm or less.
As the prior art capable of solving the above-described problems, Japanese Patent Laid-open No. 306,215/2000 discloses the technique for providing a magnetic head which cannot be deformed by heat, in order to eliminate deformation of a magnetic head on an air bearing surface (ABS) side according to an increase in temperature, reduce a floating quantity in a magnetic disk drive, and prevent any increase in danger of a crash, an increase in TA (i.e., thermal asperity) or the like.
In the technique disclosed in the above-described gazette, an insulating layer covering a coil is made of a resin, a porous member or polyimide having a glass transition point as low as from 70 to 100° C., thereby reducing thermal deformation at high humidity, or the ABS of the head is ground at the same high temperature as that in an operative state, thereby preventing any deformation or projection of the ABS during the operation.
With the above-described prior art, it has been impossible to completely prevent the projection toward the floating surface caused by the thermal deformation of the magnetic poles 15, 16, 17 and 18 made of metal, although a predetermined effect can be produced to some extent. In other words, it has been impossible to stably set the floating quantity of the magnetic head up to a height of about 10 nm, although the effect of suppression of the deformation is found. As a result of study of the cause, it is probable that the writing unit and the retrieving unit are made of different kinds of substances (i.e., metal, an insulator, resin, inorganic substance, and the like when the magnetic pole is taken as an example), and therefore, that a stress occurs between these substances different in coefficient of linear expansion if the environmental temperature is varied, thereby inducing the deformation of the magnetic head.